The present invention relates to an improvement in a nip roller apparatus for conveying objects between a drive roller and an idler roller.
As shown in FIG. 4, a conventional nip roller installation includes a drive roller 4A, an idler roller 4B pressing against the drive roller 4A, and two toothed wheels 4E, 4F mounted on shafts 4C, 4D of the rollers 4A, 4B, respectively, for transmitting rotation of the drive roller 4A to the idler roller 4B.
As best shown in FIG. 5, the shaft 4D of the idler roller 4B is supported in a bearing journal (not shown) by a bearing slide 4G (denoted by the hatching) for permitting sliding movement of the idler roller 4B. Also, the idler roller 4B is resiliently biased by a spring material (not shown) against the drive roller 4A.
The conventional nip roller installation, however, allows the idler roller 4B to press against the center of the rotation of the drive roller 4A (FIG. 5).
Therefore, if the idler roller 4B is overloaded with a strong resistance force during a conveying operation, a stress will occur on the contact surface of the toothed wheel 4F. The contact surface of each toothed wheel is arranged at an angle of pressure .alpha.. Accordingly, a counter force P of the stress is produced on the contact surface of the toothed wheel 4E. A partial or component force P1 of the counter force P acts on the idler roller 4B in a direction which opposes the pressing force of the idler roller 4B. This condition may create a difference in the nip pressure between opposite sides of the nip roller apparatus, thus causing zigzag movements of an object being conveyed by the roller apparatus.
In order to eliminate the difference in the nip pressure, a modification has been proposed in which toothed wheels are provided at both sides of the roller apparatus. However, the modification will cause increases in the dimensions and cost of the apparatus. In addition, the force of resistance on the idler roller may be increased thus attenuating the nip pressure.
It is an object of the present invention, in view of the foregoing problems, to provide an improved nip roller apparatus in which the idler roller remains unaffected by any counter forces when a resistance load is applied during a conveying operation.